Transformer-capacitor enhancement circuitry for power amplifiers

ABSTRACT

Circuitry for providing improved pulse-type enhancement of the voltage supplied to a power amplifier ( 101 ) that is fed by a power supply that is connected to the power amplifier ( 101 ) at a feeding point through a main supply path that is connected via an inductor (L 1 ). A second feeding point is used for enhancement by a capacitor that is discharged. A transformer L 2 , L 3 , M) is formed by mutually coupling an additional inductor (L 3 ), through which an additional supply path is connected. Enhancement power is provided partially through the transformer L 2 , L 3 , M) and the remaining part thorough the capacitor (C 1 ). This way, the total level of possible enhancement is increased, while minimizing distortion of the envelope of the amplified RF signal.

FIELD OF THE INVENTION

The present invention relates to the field of high efficiency poweramplifiers. More particularly, the invention relates to a circuitry forefficiently controlling the impedance at a connection point of a powersupply to a power amplifier, being a feeding point, and providingenhancement of the voltage that is delivered to said power amplifier viasupplementary supply paths that are used to connect the power supply tothat point.

BACKGROUND OF THE INVENTION

Several RF systems containing power amplifiers are characterized inrecurrent periods of signals having large peak excursions, which shouldbe handled, in order to improve the efficiency of these systems. One wayto handle signals with large peak-to-average ratios is to control the DCpower supply to a power amplifier. One voltage level is supplied to sucha power amplifier whenever the instantaneous amplitude is below a givenlevel (normal operating condition), and an enhanced (and higher) voltagelevel whenever the instantaneous amplitude is above said level. Thissolution is described for example, in WO 01/67598, which disclosescircuitry for dynamically enhancing the operating voltage of an RFamplifier. However, efficiency of the voltage enhancement circuitdisclosed therein may be further increased by controlling the impedancevalues at the connection point between the power amplifier and the powersupply, during normal operation and during voltage enhancement timeperiods.

It is therefore desired to allow a power amplifier to work underdifferent operating power supply voltages, in response to differentinput signals or conditions under which the power amplifier, or acomponent contained within it, operates. For example, in order tooptimize the operation of a power amplifier, it has been foundbeneficial to provide it with a DC power through a first supply pathwhenever the signal at its input is below a predetermined level, and adda second and a third supplemental power supply paths at instants whereinthe signal at its input is above that level, thus enhancing theeffective voltage supplied to said power amplifier. This type ofsolution allows operating a power amplifier in a relatively largedynamic range with high efficiency, as the enhanced operating voltagesource is coupled to the circuit only when required by the largeinstantaneous amplitude.

U.S. Pat. No. 6,831,519B2 discloses circuitry that allows efficientenhancement of the voltage supplied to a power amplifier during requiredtime periods. This circuitry controls the level of the voltage suppliedto a power amplifier, via a supplementary supply path that is connectedto the feeding point, during both the enhancement period, and periods ofnormal operation (also called “normal period”). However, the level ofenhancement provided by the circuitry of has not been sufficient formore high power applications. In addition, in the circuit of U.S. Pat.No. 6,831,519 the enhancement current is provided by a couplingcapacitor, which has a limited capability to pass low frequencycomponents of the enhancement pulse.

It is therefore an object of the present invention to provide improvedcircuitry that allows efficient enhancement of the voltage supplied to apower amplifier during enhancement periods, while minimizing envelopdistortion of the amplified RF signals.

It is another object of the present invention to provide improvedcircuitry for efficiently controlling the level of the voltage suppliedto a power amplifier, via two supplementary supply paths that areconnected to the feeding point, during both the enhancement period, andperiods of normal operation.

It is another object of the present invention to provide improvedcircuitry for efficiently controlling the impedance at that feedingpoint in the direction of the power amplifier and of the supplementarysupply path, during both the enhancement period, and the normal period.

Other objects and advantages of the invention will become apparent asthe description proceeds.

SUMMARY OF THE INVENTION

The present invention is directed to an improved method for allowingimproved pulse-type enhancement of the voltage supplied to a poweramplifier fed by a power supply being connected to the power amplifierat a first feeding point through a main supply path connected via afirst inductor having a high impedance to an enhancement pulse at thefeeding point, and to a second feeding point. A first supplementarysupply path is used for providing enhanced operating voltage to thepower amplifier that is connected to a first power supply. A pair of afirst and a second controllable impedances that are connected by acommon contact is provided and have a separate control input and beingcapable of being in a non-conducting state is also provided. At leastone of them is capable of being in a desired variable level ofconduction up to full conduction. A second supplementary supply path isused for providing enhanced operating voltage to the power amplifier,through a second inductor that is connected to a second power supply andto the common contact. One contact of the first controllable impedanceis connected to the second feeding point, while the first power supplyis connected across the contacts of the pair which are not connected tothe common contact. A capacitor is connected between the common contactand the first feeding point and an inductive pair is formed bygenerating mutual coupling between the first and second inductors.

During the time period when no enhancement is required, the firstcontrollable impedance is controlled through its separate control input,to be in its conducting state and effectively connect the common contactto the second feeding point of one of the first power supply and thesecond power supply. At the same time, the second controllableimpedance, is controlled through its separate control input, to be inits non-conducting state. The common contact is effectively disconnectedfrom the second feeding point and the capacitor is charged toessentially the voltage of the power supply.

during the time period when enhancement is required, the firstcontrollable impedance is controlled through its separate control input,to effectively disconnect the common contact from one contact of powersupply. At the same time, the second controllable impedance iscontrolled through its separate control input, to be in a conductionlevel that corresponds to a desired enhancement voltage level at thefirst feeding point, such that a portion of the required enhancementpower is supplied by the inductive pair and another portion is suppliedby the capacitor. By doing so, the magnitude of the voltage at thecommon point, to which a contact of the capacitor is connected, isincreased, while causing an essentially similar increase in the voltageat the first feeding point, to which the other contact of the capacitoris connected, up to the desired enhancement voltage level. The inductorsforming the pair may be wound on the same core, so as to form atransformer.

The present invention is directed to a circuitry for providing improvedpulse-type enhancement of the voltage supplied to a power amplifier fedby a power supply being connected to the power amplifier at a firstfeeding point through a main supply path connected via a first inductorhaving a high impedance to an enhancement pulse at the feeding point,and to a second feeding point, that comprises:

-   -   a) a first supplementary supply path for providing enhanced        operating voltage to the power amplifier connected to a first        power supply;    -   b) a pair of a first and a second controllable impedances being        connected by a common contact, each of which having a separate        control input and being capable of being in a non-conducting        state, and at least one of which is capable of being in a        desired variable level of conduction up to full conduction, such        that one contact of the first controllable impedance is        connected to the second feeding point and the first power supply        is connected across the contacts of the pair which are not        connected to the common contact;    -   c) a second supplementary supply path for providing enhanced        operating voltage to the power amplifier, through a second        inductor, connected to a second power supply and to the common        contact;    -   d) a capacitor, connected between the common contact and the        first feeding point; and    -   e) an inductive pair, formed by generating mutual coupling        between the first and second inductors.

The circuitry is configured such that during the time period when noenhancement is required, the first controllable impedance is controlledto be in its conducting state and effectively connect the common contactto the second feeding point of one of the first power supply and thesecond power supply, and the second controllable impedance is controlledto be in its non-conducting state and thereby, effectively disconnectingthe common contact from the second feeding point and allowing thecapacitor to charge to essentially the voltage of the power supply; and

The circuitry is also configured such that during the time period whenenhancement is required, the first controllable impedance is controlledto effectively disconnect the common contact from one contact of the, oranother power supply, and the second controllable impedance iscontrolled to be in a conduction level that corresponds to a desiredenhancement voltage level at the first feeding point, such that aportion of the required enhancement power is supplied by the inductivepair and another portion is supplied by the capacitor.

The controllable impedance may comprises a bipolar transistor or a FET.The first and second inductors are wound on the same coil, so as to forma transformer.

Preferably, during the time period when enhancement is required, thefirst and/or the second controllable impedances are controlled by pulsesignals having a duration which is essentially similar to the timeperiod.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other characteristics and advantages of the invention willbe better understood through the following illustrative andnon-limitative detailed description of preferred embodiments thereof,with reference to the appended drawings, wherein:

FIG. 1 is a block diagram of a circuitry that controls the level ofenhancement of the voltage supplied to a power amplifier, according toprior art;

FIG. 2 schematically illustrates an implementation of a circuitry thatcontrols the level of enhancement of the DC power that is supplied to apower amplifier according to prior art; and

FIG. 3 schematically illustrates the implementation of a circuitry thatincludes additional supplementary path to better control the level ofenhancement of the DC power that is supplied to a power amplifier,according to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of a circuitry that controls the level ofenhancement of the voltage supplied to a power amplifier, according toprior art. The power amplifier 101 is supplied with operating voltagethrough a feeding point x, which is connected to a DC voltage supply 102via the main supply path 103, and to a voltage enhancement pulse source100, via a supplementary supply path 104. The Voltage Enhancement (VE)circuitry 100 increases the supply voltage at the feeding point x for arelatively short duration (in the order of the reciprocal of themodulation bandwidth), when voltage enhancement is required. Undernormal operation conditions (i.e., when no enhancement is required), thefeeding point x has an extremely low resistance to the DC current i₁consumed from the DC voltage supply circuitry 102 (in the direction D1).During the same normal operation period, the VE pulse source 100 causesfeeding point x to have an extremely low impedance to all the frequencycomponents of the fluctuating current i₂ generated by the poweramplifier 101.

According to a preferred embodiment of the invention, during therelatively short duration when a (large) peak in i₂ is required, the VEpulse source 100 issues a VE pulse and the DC voltage supply 102concurrently allows the feeding point x to have a high impedance in thedirection D2, such that the VE pulse is fully directed into the poweramplifier 101, rather than being short-circuited into the DC voltagesupply 102. Therefore, during the VE period the effective current i₁+i₂,supplied to the power amplifier 101 comprises an enhanced component i₂,as required by the large instantaneous amplitude of the RF signalamplified by the power amplifier 101.

FIG. 2 schematically illustrates an implementation of the circuitry ofFIG. 1, according to prior art. The VE circuitry 100 consists of twoserially connected controllable impedances and (e.g., FETs or bipolartransistors), which are also connected between the contacts of the powersupply V_(DC) ₁ , or of a supplementary power supply V_(DC) ₂ . Thepower supply V_(DC) ₁ , used to supply power to the power amplifier 101under normal operation conditions, is connected to the feeding point xthrough a serial inductor L₁, which is selected to introduce extremelyhigh impedance to the issued VE pulse, in the direction D2. The commonpoint of controllable impedances Z1 and Z2 is connected to the voltagesupply feeding point by a capacitor C₁. The value of C₁ is selected tointroduce low impedance to all the frequency components of thefluctuating current generated by the power amplifier 101. In addition,the value of C₁ should be sufficiently large for supplying the excesscurrent i₂ for the (short) duration when the VE pulse is issued. Duringnormal operation, the fluctuating components of i₂ flow throughcapacitor C1.

Controllable impedances Z1 and Z2 are implemented in this example usingField-Effect-Transistors (FETs), each of which is properly biased by aninductor L₂ (which also serves as a choke for the exciting pulses, P1and P2) connecting their gates to the biasing voltages V_(B1) andV_(B2), respectively. Controllable impedances Z1 and Z2 are controlledby separate control pulses, P1 and P2, respectively, throughcorresponding serial capacitors C2, which serve as DC-blocks (in orderto isolate the control signals from the biasing voltages V_(B1) andV_(B2).

V_(B1) is selected such that during normal operation conditions, Z1 isin full conduction, effectively short-circuiting point y to ground bybecoming a negligible impedance to ground. V_(B2) is selected such thatduring normal operation conditions, Z2 is effectively an open-circuit.In this state, the supplemental V_(DC) ₂ is essentially disconnectedfrom the feeding point x. Consequently, i₂ flows through C1 and Z1 toground, as required for proper operation of the power amplifier 101,while i₁ flows through capacitor C1. Simultaneously, capacitor C1 ischarged to a voltage that essentially equals V_(DC) ₁ .

When VE is required, Z1 is forced by P1 to enter into its non-conductingstate, having effectively infinite impedance, thereby effectivelydisconnecting C₁ from ground. Simultaneously, Z2 is allowed to be in aconducting level that corresponds to the amount of VE that is required,by properly controlling the level of P2. This allows the voltage atpoint y to rise above zero and by virtue of capacitor C1, to enhance thevoltage at point x. At this stage, C1 discharges into the poweramplifier 101 through the feeding point x, thereby causing thesupplemental current i₂ to flow in direction 22 for the duration of thecontrol pulse P₂. The level of enhancement depends on the value of theimpedance R_(DS) ₂ (i.e., the impedance of Z2 while being in theappropriate conducting measure). Lower value of R_(DS) ₂ results inhigher level of enhancement. The duration of the VE pulse is determinedby the duration of the control pulse P2. The voltage level V_(X) at thefeeding point x increases at the switching moment by a level determinedby R_(DS) ₂ and the value of V_(DC) ₂ . The maximum value of enhancementis obtained when R_(DS) ₂ =0 and when V_(x) equals the sum of thevoltage V_(DC) ₂ and the voltage across capacitor C1, which is V_(DC) ₁+V_(DC) ₂ . During the VE period, capacitor C1 discharges slightly,while participating in the VE process.

After the enhancement period is terminated, that is the control pulsesP1 and P2 are terminated and Z2 returns to its non-conducting state.Concurrently, Z1 is controlled to re-enter its conducting state, alsoallowing C1 to recharge via path 23 to V_(DC) ₁ and be ready for thenext required VE period.

FIG. 3 schematically illustrates an improved implementation of thecircuit illustrated by FIG. 1, according to a preferred embodiment ofthe present invention. An ancillary low voltage power supply V_(DC3) isconnected to by adding an inductor L₃. During normal period, the DCcurrent I₃ that flows through L₃ continues to ground via thecontrollable impedance Z₁. During an enhancement period when the pathtrough Z₁ is blocked by a pulse P1, part of I₃ is diverted to flow, viaC₁, into the RF amplifier. The additional inductor L₃, possibly wound onthe same core as inductor L₁ to form a transformer with mutual couplingM, is connected on one side to the common point y of the controllableimpedances Z1 and Z2 and on the other side to the additional powersupply V_(DC3). Here, when I_(PA) is at its quiescent value (i.e., noenhancement) and has no fluctuations, i₃ equals i₅ and flows to groundvia Z1. The value of the voltage V_(DC3) equals i₃ times R_(DS1), whichis a very low voltage, due to the fact that Z1 is in its conductingstate. The advantages owed to the thus-formed second supplementary powerpath will be illustrated while considering the currents identified inFIG. 3.

In the case that the inductors L₁ and L₃ are wound on different cores,that is M=0, i₁ as well as is are forced to remain practically constanteven during an enhancement pulse. During normal period, the varyingcomponent of the Power Amplifier current I_(PA) flows via capacitor C₁and is subtracted from i₅. During enhancement period, when I_(PA) needsto be very large, pulse P₁ restricts the current i₅ even more, such thata part or even all of i₃ contributes to the increased I_(PA). At fullenhancement, i₅ becomes zero and pulse P₂ enables the largest i₄ to flowand therefore I_(PA)=i₁+i₃+i₄.

In the case that L₃ and L₁ are wound on the same core, such that L₁=L₃=Land M is close to L, a transformer is formed and only the sum i₁+i₃ isforced to remain practically constant. Thus, i₁ can increase if i₃decreases and vice versa. Then, during the enhancement period,fluctuations in I_(PA) can still flow via L₁ until all the current i₃ isexhausted for satisfying the requirement of i_(PA). If the enhancementneeded is above this value, the i₄ current through C₁ is needed tosupply I_(PA)=i₁+i₃+i₄. Therefore, the enhancement is provided partiallythrough the transformer and the remaining part thorough the couplingcapacitor C₁. This way, the total level of possible enhancement isincreased, while minimizing distortion of the envelop of the amplifiedRF signal, since low frequency components of the enhancement pulse aretransferred to the output of the enhancement circuitry by thetransformer, while high frequency components of the enhancement pulseare transferred to the output of the enhancement circuitry by C₁.

The above examples and description have of course been provided only forthe purpose of illustration, and are not intended to limit the inventionin any way. As will be appreciated by the skilled person, the inventioncan be carried out in a great variety of ways, employing more than onetechnique from those described above, all without exceeding the scope ofthe invention.

1. A method for allowing improved pulse-type enhancement of the voltagesupplied to a power amplifier fed by a power supply being connected tosaid power amplifier at a first feeding point through a main supply pathconnected via a first inductor having a high impedance to an enhancementpulse at said feeding point, and to a second feeding point, comprising:a) providing a first supplementary supply path for providing enhancedoperating voltage to said power amplifier connected to a first powersupply; b) providing a pair of a first and a second controllableimpedances being connected by a common contact, each of which having aseparate control input and being capable of being in a non-conductingstate, and at least one of which is capable of being in a desiredvariable level of conduction up to full conduction; c) providing asecond supplementary supply path for providing enhanced operatingvoltage to said power amplifier, through a second inductor, connected toa second power supply and to said common contact; d) connecting onecontact of said first controllable impedance to said second feedingpoint; e) connecting said first power supply across the contacts of saidpair which are not connected to said common contact; f) connecting acapacitor between said common contact and said first feeding point;forming an inductive pair by generating mutual coupling between saidfirst and second inductors; g) during the time period when noenhancement is required, simultaneously and separately controlling saidfirst controllable impedance through its separate control input, to bein its conducting state and effectively connect said common contact tosaid second feeding point of one of said first power supply and saidsecond power supply, and controlling said second controllable impedance,through its separate control input, to be in its non-conducting stateand thereby, effectively disconnecting said common contact from saidsecond feeding point and allowing said capacitor to charge toessentially the voltage of said power supply; h) during the time periodwhen enhancement is required: i) controlling said first controllableimpedance, through its separate control input, to effectively disconnectsaid common contact from one contact of said, or another power supply;and j) simultaneously and separately, controlling said secondcontrollable impedance, through its separate control input, to be in aconduction level that corresponds to a desired enhancement voltage levelat said first feeding point, such that a portion of the requiredenhancement power is supplied by said inductive pair and another portionis supplied by said capacitor, thereby increasing the magnitude of thevoltage at said common point, to which a contact of said capacitor isconnected, and thereby causing an essentially similar increase in thevoltage at said first feeding point, to which the other contact of saidcapacitor is connected, up to said desired enhancement voltage level. 2.A method according to claim 1, wherein the inductors forming the pairare wound on the same core, so as to form a transformer.
 3. Circuitryfor providing improved pulse-type enhancement of the voltage supplied toa power amplifier fed by a power supply being connected to said poweramplifier at a first feeding point through a main supply path connectedvia a first inductor having a high impedance to an enhancement pulse atsaid feeding point, and to a second feeding point, comprising: a) afirst supplementary supply path for providing enhanced operating voltageto said power amplifier connected to a first power supply; b) a pair ofa first and a second controllable impedances being connected by a commoncontact, each of which having a separate control input and being capableof being in a non-conducting state, and at least one of which is capableof being in a desired variable level of conduction up to fullconduction, such that one contact of said first controllable impedanceis connected to said second feeding point and said first power supply isconnected across the contacts of said pair which are not connected tosaid common contact; c) a second supplementary supply path for providingenhanced operating voltage to said power amplifier, through a secondinductor, connected to a second power supply and to said common contact;d) a capacitor, connected between said common contact and said firstfeeding point; e) an inductive pair, formed by generating mutualcoupling between said first and second inductors; said circuitry isconfigured such that during the time period when no enhancement isrequired: said first controllable impedance is controlled to be in itsconducting state and effectively connect said common contact to saidsecond feeding point of one of said first power supply and said secondpower supply, and said second controllable impedance is controlled to bein its non-conducting state and thereby, effectively disconnecting saidcommon contact from said second feeding point and allowing saidcapacitor to charge to essentially the voltage of said power supply; andsuch that during the time period when enhancement is required: saidfirst controllable impedance is controlled to effectively disconnectsaid common contact from one contact of said, or another power supply,and said second controllable impedance is controlled to be in aconduction level that corresponds to a desired enhancement voltage levelat said first feeding point, such that a portion of the requiredenhancement power is supplied by said inductive pair and another portionis supplied by said capacitor.
 4. Circuitry according to claim 3,wherein the controllable impedance comprises a bipolar transistor. 5.Circuitry according to claim 3, wherein the controllable impedancecomprises a FET.
 6. Circuitry according to claim 3, wherein said firstand second inductors are wound on the same coil, so as to form atransformer.
 7. Circuitry according to claim 3, wherein during the timeperiod when enhancement is required, the first and/or the secondcontrollable impedances are controlled by pulse signals having aduration which is essentially similar to said time period.